Light Perception One major type of response to light in plants is phototropism (from the Greek tropos,“turn”), growth toward or away from light 1. Growth toward light is known as positive phototropism (shoots) 2. Growth away from light is known as negative phototropism (roots)

No light Growth Response Light does not cause auxin degradation but rather changes its distribution 1. In shoots this promotes growth on the side with higher auxin concentrations 2. In roots high auxin concentrations inhibit growth and therefore the dark side of the root grows less Auxin concentration

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Flowering Time 1. The nature of the cellular component that measures night length is not known 2. Phytochrome itself does not serve this function 3. By the end of the night P FR has decayed back to P R 4. It is thought that a subpopulation of phytochrome molecules may be involved in measuring night length

Transmitting the Message 1. FT protein is synthesized in leaves and transmitted to the SAM 2. In the SAM, FT protein acts together with a transcription factor, FD, to initiate floral development mRNA SAM FT mRNA FD FT Protein

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